Electrostatic telephxmca



J. MASSOLLE ELECTROSTATIG TELEPHONIC INSTRUMENT FOR TRANSMITTING OR RECEIVING PURPOSES nm 2 9 1l.

original Filed Aug. 5, 1925 Re 17,256

Reiaaued pr. 2, 1929. A

UNITED STATES 10mn IASSOLLE, OF BEBLIN-WILMERSDORF, GERMANY, ASSIGNOR TO TBI-EBGON Re. 17,256 PATENT OFFICE.

A. G., OI' ZURICH, SWITZERLAND, A CORPORATION OF SWITZERLAND.

ELECTROSTATIC TELEPHONIC INSTRUMENT'TOR TBANSMITTING OB RECEIVING PURPOSES.

Uglnal No. 1,609,760, dated December 7, 1926, Serial No. 47,662, led August 3, A1921i, and in Gcriuany July 9, 1985. Application for reissue led February 20, 1929. Serial No. 341,547.

, T hisinvention relates to improved electrostatlc telephonie instruments for transmittin`g or receivinpurposes and more particularly or prefera ly to a so-calledloud-speakmg receiver.

It is a known fact that a perfectly true sound reproduction free from disturbing resonance notes and distortions or deformations cannot be obtained in a satisfactory manner except by means of apparatus which work on the electrostaticprinciple. In contradistinction thereto all o the apparatus whichat present are usually practised and y in which the alternating currents are transformed into sound waves according to the electromagnetic principle, are very objectionable. y

The reason of the superiority of the yapparatus `working on the electrostatic principle resides in that heavy and lstron *'phragms need not be employed terein and,

as contrasted with magnetic loud-speaking receivers, funnel-shaped 'amplifying horns vare not required order to ensure a coupling with a qu tity of air 'sufficient to realize a loud sound reproduction. For

electrostatic loud-speaking receivers of the.

kind, as is well known in the art, allow of employing or applying larger diaphragm surfaces so that such surfaces are sufficiently coupled with the air.

An object of. this invention is to improve the electrostatic instruments for transmitting or receiving purposes, particularly louds aking receivers having tightly stretched dlizphragms, as hitherto constructed, by stretching the latter into their ellicient position and holding the same in suchv position by means of the capacity body, or'in other words, by positively forcing the capacity body mounted on the diaphragm holder, toward the. diaphragm andy securing the body in the holder with the diaphragm in properly stretched position. Other objects of the invention consist in the provision of improved forms of construction and combinations of elements, all as will more fully ap `ear in the following specification. y

Xn electrostatic instrument constructed according to the present invention, therefore` mainly comprises a rigid capacity body, a v,very thin diaphragm or film in front of thc former and a short distance apart therefrom only, and a diaphragm holder, the two faces of the diaphra m or film being absolutely plane and paral el to each other and oneface being coated with an electric conductor as usually.

In practically using an electrostatic instrument especially loudspeaking receiver cf the improved construction the alternatlng voltages lie between the electric conductor or coating ofthe diaphragm and the capacity body. The variation of voltage results in a variation ofthe electrostatic forces of attraction between diaphragm and capacity body. The diaphragm vibrates according to the rhythm of the-alternating voltages and roduces in this way corresponding sound) waves.

According to the vpresent invention the diaphragm preferably consists of an extremely thin mica film with a metallic coating thereon and the holder preferably consists oftwo rings adapted to be firmly con nected to each other with the diaphragm interposed therebetween so as to be perfectly plane. The two rings constituting the diahragm holder are connected with each other y means of screws or the like and they are shaped-in section-in a manner that, upon tightening the screws, the diaphragmperipherally interposed between the two. halves of the holder, will receive a preliminary stretching in radial respects so that the same will be perfectly 4fiat and plane.

The thus obtained preliminary stretching of the diaphragm is eiciently completed preferably' in the following way. The ri 'd capacity body is provided with a contacting member or surface co-operating with the film or diaphragm and situated suliiciently remote from or above the active surface of the capacity body t cause the diaphragm, upon tightening the screws provided for connecting thecapacity'hody to the holder to be displaced from its previous fiat condition or plane without changing 1or interfering with the requisite distance between the innerface of the diaphragm; and the opposed face of the capacity body or with the parallelism of the active surface ofthe latter and the diaphragm. In other words, by connecting theimproved capacity body with the bipartite holder by means of screws a means will be afforded for giving thediaphragm the Azo . phragm is clamped between t e requisite stretching and tension by displacing the same with respect to the holder but without displacing the same with relation to the capacity body.

With the above recited and other object in view, theinvention resides in the novel construction set forth in the following specification, particularly pointed out in the appended claims and illustrated in the accompanying drawings, it being understood that the ri ht is reserved to embodiments other than those actually illustrated herein to the full extent indicated by the general meaning of the terms in which the claims are expressed.

In the vaccompanying drawings forming a part of this specification a single example or embodiment of the invention is exhibited, Figure 1 being a view in axial or central section of the diaphragmwholder with the diaphragm clamped, between the two parts thereof, in its preliminary stretched position; Figure 2 being a similar sectional view of thecapacity body; and Figure 3 showing the two components illustrated 'in Figures 1 and 2, duly assembled and with the dia-` phragm in fully tensioned condition.

Referring to Figure 1 the thin mica film 1 is provided on its outer face with an electrically conducting, preferably metallic coating 2 and the peripher of the diatwo rings 3 and 4 which constitute the holder, these rings being of like dimensions in diametri-y cal respects. The inner edge 5 of the inner periphery of the ring 3 is rounded, whilst the inner edge of the outer periphery of the ring 3 is shaped to form an annular flange 11. The two rings 3 and 4 are to be connected with each other, in superposed relation and with the peripheral ortion of the diaphragm 1 therebetween, y means of screws 6. By tightening the latter-the two rings willapproach eac-h other and, owing tothe particular shape of the ring 3 and the springiness ensured by such shape, the dia-4 phragm 1 will be-radially drawn outwards and thereby receive a preliminary stretching to form an accurately plane surface as shown in Figure l.

lThe circular or disk-shaped'capacity body comprises a central portion 19, a peripheral or rim portion 8 and an intermediate portion 7 which is thoroughly plane on both sides and of even thickness throughout. The three portions constituting the capacity body are preferably made in one piece so as to be integral with each other. The rim 8 comprises a mainportion 9 which is of the same thickness, in axial regards, as the central portion 19, and an annular fiange 10 projecting from the portion 9 outwards or 1n radial directions so that'the two parts 9 and 10 are perpendicular to each other. The annular flangev 1()"is provided with a The central portion 19 of the capacity vbody is cup-shaped to accommodate an annular disk 17 filling the cup to the level of the intermediate portion 7 of the body, and the bottom of the cup isenlarged to form a boss 2O with a central threaded bore for the reception of a short spindle or screw 18 the purpose o f which will be explained further below.

On the top of the described capacity body two flat rings l5 and 16 made of a non-conducting material such` aspaper or the like, are placed, the larger ring 15 being supported by the portion 9 of the rim 8 and the narrower ring 1G being I'supported by the disk 17 which fits loosely in the cup or cavity of the central portion 19 of the capacity body.

The dimensions of the ring 4 of the holder and of the portion 9.of th rim 8 of the capacity body are selected to render the distance a, Figure 1, between the lower or inner surface of the mica diaphragm and the edge '14 ofnthe ring 4 somewhat less than the distance b, lFigure 2, between the top of the bushesf12 and the plane of or coincidingv with the upper faces of the paper or other insulating rings 15 and 16, so that upon assembling and connecting together the holder and the capacity body by means of the screws 13 the insulating rings 1 5 and 16 will displace and lift the mica diaphragm out of. its position, shown in Figure 1, into a parallel plane, a; shown in Figure 3. In this way the requisite tension of thediaphragmis brought about and the paper rings 15 and 16 act to prevent the properly stretched and tensioned diaphragm from contact-ing with the intermediate portion 7 of the capacity body, when caused to `vi brate. The extent to which the diaphragm 1 is'removed or lifted from the plane position shown in Fig. 1 to the elevatedposition illustrated in Figure 3, that is, the stretching or final tension of the diaphragm, therefore, is determined by the difference between the dimensional values aand b, Figures 1 and 2.

For the purpose of adjusting the diaphragm 1 with relation to the opposed surface of the capacity body I provide the disk so-that the latter can be firmly conthe spindle or screw 18, as hereinbefore described. By means of the spindle or screw 18 and disk 17 can he raised above the level or plane of the intermediate portion 7 of the capacity body whereby the ,paper ring 1G will be lifted out of the plane otthe paper ring 15 and the diaphragm 1 correspondingly spaced apart from the capacity body to the desired or required extent.

In order to maintain the tension of the diaphragm, obtained in the manner hereinbefore described, constant for any length of time, it is advisable to use a material for making the two clamping rings 3' and 4, which possesses the very same coeliicientI of expansion. as the material of which the diaphragm is made or consists. Thus if the diaphragm consists of mica, clamping rings 3 and 4 made of suitable east iron will give satisfactory results on the line labove indicated it being possible to reduce, by selectin a cast iron of the required properties, the di erence `between the coeicients of expansion of the two materials, viz, mica and cast iron, so far as to realize and ensure a tension in the diaphragm which is practically constant or independent of variations of temperature.

The intermediate portion 7 of the capacity bod may be provided with perforations 21 pre erably arranged symmetrically'all' over the annular portion 7, for the purpose of reducing the damping in the narrow space between the diaphagm and the capacity body.

1. In an electrostatic telephone, the' combination of a diphragm holder, a diaphragm,

means for securing said diaphragm in saidholder, a rigid plate constituting a capacity bod and means :for securing said plate ,-to saidy holder, after said diaphragm is secured in' said holder, in such position that said plate will exert pressure againstsaid diaphragm, within said holder, to stretch the diaphragm.

2. In an electrostatic telephona'the combination of a diaphragm holder, a diaphragm, means for securing said diaphragm in said holder, a rigid plate constituting a capacity body having a pressure device associated therewith, and means for securing said plate rigidly to said holder, after said diaphragm is secured in said holder, in such position that said pressure device will bear against said diaphragm, within said holder, to displace it from the plane occupied thereby previous to the securing of said plate in position, to stretch the diaphragm.

3. In an electrostatic telephone, the combination of .a pair of rings constituting a diaphragm holder, a diaphragm, means for securing the same between said rings, a rigld plate constituting a capacity body, carrying a pressure device, and having an oiset outer ange, and means for securing 4said flange againstone of'saidrings,aftersaiddiaphragm has been secured in said holder, with said pressure device bearing against'said diaphragm, within said holder, to stretch said diaphragm. 1

4. In an electrostatic telephone, the combination of aipair of rings constituting a diaphragm holder, a diaphragm, secured between said -rings, a rigid plate constituting a capacity body, having a forward face and a rearwardly extending niarginaliange with an outwardly extending offset portion, spacing means to be positioned between said torward face and said diaphragm, and means for securing said ange offset portion against one of said rings with said spacing means bearing against ,said diaphragm to stretch the same.

5. In an electrostatic telephone, the combination of one unit comprising a diaphragm and rigid ring secured to the edge thereof, a second unit comprising a rigid condenser plateand seating means therefor extending radially`outwards to the rearof said plate, and rigidly connected thereto, and means for securing said seating'means against said ring with said plate exerting pressure against said diaphragm within said ring to stretch the same.

6. In an electrostatic telephone, the com bination of a unit comprising a diaphragm and rigid ring secured to the'edege thereof,

a rigid condenser plate,seating means therefor ri idly connected thereto and extending `radial y outwards to the rear thereof, spacing means on the edge'and center of said plate. and means for securing said seating nic-ans against said ring with said plate extending within said ring *and said spacing means exertingpressure against said diaphragm to stretc the same.

7. In an electrostatic telephone, the combination of a holder, .a diaphragm having its edge secured thereto, a rigid condenser plate,.seating means therefor rigidly connected thereto and extending radially out- `wards to the rear thereof, spacing means extending through said plate and adapted to be positioned at an adjusted distance beyond the face of said plate, and means for securing said seating means against said holder with said plate extending within said holder and exerting pressurejagainst said diaphragm to stretch the same.

8. In an electrostatic telephone, the combination of a holdercomprising a pair of rings, and a diaphragm lsecured at its edge between the same, saidrings being arrange to place said diaphragm under preliminary tension, a rigid condenser plate, rearwardly spaced marginal seating means therefor,

and means :for securing said seating means against one of said ringsi with said 'plate exerting pressure against said diaphragm to place the same under tension greater than said preliminary tension.

to stretch the diaphragm as secure 9. In an electrostatic telephone, the combination of a diaphragm holder, a diaphragm, means for securing said diaphragm in said holder, a rigid plate constituting a capacity body and means for securing said late to said holder, in such position that saidplate will exert pressure against said dia hra 1n, wit in said holder.

10. An electrostatic telephone, comprising a diaphragm, a rigid condenser plate member, and means at the periphery of said rigid plate -member for peripherally securing the diaphragm in respect thereto with portions at the face of said rigid plate member exerting pressure against the diaphragm within said diaphragm securing means for displacing the entire effective vibratory area of the diaphragm from the plane of its secured periphery, to stretch the* diaphragm over the face of said rigid plate.

11. In an electrostatic telephone, the combination of a diaphragm holder, a diaphragm, means for securing said diaphragm in said holder, a rigid plate constituting a capacity Falong predetermined lines only, .to maintain the diaphragm stretched as secured within said holder, said rigid plate having perfo- -rated capacity areas between said lines.

12, An electrostatic telephone, comprising a diaphragm, a rigid condenser plate member, and means at the periphery of,l said rigid plate member for securingedges of the diaphragm in respect thereto With portions at the face of said rigid plate member exerting pressure along predetermined lines against thewdiaphragm as mounted in said dlaphragm securing means, for displacing the e'ective vibratory areas of the diaphragm from the plane of its said secured edges, to maintain the diaphragm stretched over the face of said ri id plate, said rigid plate having perforate capacity areas between said predetermined lines.

In testimony whereof, I have signed my name to this petition.

JOSEPH MASSOLLE. 

